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Mercruiser 454 or 7.4 Serial numbers

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Old 04-26-2007, 05:42 PM
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Default Mercruiser 454 or 7.4 Serial numbers

On StemtoStern.com, or Mercruiserparts.com, or other parts lookup websites, there is a range of serial numbers from about 0f800000 to 0k999999.

If you were looking at stern drive big blocks, these numbers were identified as ........1996-97 454 Mag MPI (Gen IV)
If you were looking at inboard big blocks, these numbers were identified as .........1996-97 7.4L MIE MPI (Gen IV).

But they are all (stern or inboard) in the same category of numbers.

Do all these engines have rectangle ports and HiPerf cam?
What hp are these engines?
Are they all the same (except for the bellhousing)?

Some people say they are 300HP, some say that they are 385HP.
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Old 04-26-2007, 06:38 PM
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454 mag mpi is 385 hp 7.4 mpi is 310 i believe. the 7.4 model has weak internals. I do not know about the heads.
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Old 04-26-2007, 08:23 PM
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The part numbers for the 7.4 MIE MPI are:
Crank.............429-811551
Head...............938827656
Intake.............805233A6

The numbers for the 454 Mag MPI are:
Crank..............737-850477T
Head...............938-827495T
Intake..............805233A6

So, the cranks are different.
The Heads are different.
But the intake is the same.
Did Merc put a rectangle MPI intake on oval heads?
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Old 04-27-2007, 05:38 PM
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How can these engines have different part number for heads but have the same intake?
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Old 04-27-2007, 06:13 PM
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Quote:
Originally Posted by jerosejr View Post
How can these engines have different part number for heads but have the same intake?
The 7.4MPI's (pre L29) used the MPI intake with the retangular runners but it was bolted up to the small oval port heads. Seems crazy, but that's what they did.

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Old 04-27-2007, 09:11 PM
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Is this confirmed because there are a lot of engines for sale on OSO, Ebay, etc that have a serial number in this range and people are claiming 400 HP, probably because they figure that a Gen VI with rectangular MPI MUST be Hi Performance.


Well, what about all the problems you see on this forum regarding fuel pooling, etc.
Did Merc just decide this was not a problem?
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